The object of the invention is a mechanism of simple construction and maintenance attaining the higher efficiency without any risk of impairing safety during flight, with the command of operations related to the directional control, i.e., control of the cyclic pitch and collector or collective pitch in order to generate the desired movements in the helicopter.
Mechanisms of the mentioned kind are already known in the art, allowing the manual control of the blades from the cabin in order that the helicopter may change its direction, and the constitutive and structural features of which cause disturbing effects on the vehicle stability due to the size or dimension of the components or due to the effect of undesired forces tending to incline the apparatus or to produce undesirable oscillations.
The command mechanism of helicopters is one of the most complex parts thereof as it should accomplish a complex function since the flight of this type of machines is different from that of conventional airplanes. In fact, helicopters are supported by means of the movement of a rotor the blades of which are manually controlled from the cabin.
Vertical support is created by a combination of the rotor revolution increase and the blades pitch.
The displacement or change of direction is obtained by inclination of the complete rotational circular plane formed by the rotor blades during their rotation, this allowing the helicopter to fly forwardly, rearwardly or towards the sides.
For a better understanding of the movement created as a consequence of the angle of attack of the blades, it is to be noted that the blades are related to the rotor mast, such that they may move vertically without affecting the mast, i.e. they have a movement known as fluttering. Apart from this type of fluttering hinge, they have a strong or resistant hinge, allowing slight movement of the blades forwardly and rearwardly, at the base height (root height), place on which they are hinged to the mast, thus avoiding fatigue cracks.
This kind of articulated rotor whose blades, individually or jointly may flutter, resist forward movement or rout, is commanded by a universal mechanism in helicopters called "circular ring" or "oscillating plate", which transmits command movements for producing cyclic or collective pitch variation to the blades.
Upon operating the cyclic pitch command, known as "lever", which is in front of the pilot into the cabin, the displacement of the helicopter is controlled as per its longitudinal or transversal axes and, when the pitch or collective command at the left of the pilotis actuated, displacement of the helicopter is controlled through its vertical axis.
An appropriate combination of both commands, i.e. of the cyclic and collective pitches with the force caused by the anti-torque rotor, enables the whole control of an helicopter.
As already mentioned, the universal mechanism allowing the control or transmission of the pitch to the blades is known as "oscillating plate", which although efficient for its specific function, has certain disadvantages due to the size of its parts and of the effects resulting from such size since, as known, any rotatory mass produces a gyroscopic effect when trying to make its rotation in a plane different from the common rotational plane, as happens when a force is created at a determined point of the rotational plane by means of linkages when acting the corresponding commands.
The mechanism called "oscillating plate", as may be seen in FIGS. 13-14 comprises a hub (1) acting as a jaw fixed to the mast (2) to which mast (4) blades (3) are hinged, by means of flexing portions (5), in order to effect a semi-rigid movement around its flapping axis (a). The blades (3) are connected to corresponding rocker arms (6) connected to the base of blades (3) to allow the smooth rotation thereof around pitch change spindles (7).
Rocker arms (6) are pivotally interconnected by means of connecting rods (8) to an oscillating plate (9), comprising a rotatory portion (9a) and to a fixed portion (9b) connected by means of rods (10) to the cyclic command lever (11).
In turn, the fixed portion (9) is related to means transmitting, when the collective pitch command (12) is activated, a movement which is added to the movement of the cyclic pitch command, raising or lowering the oscillating plate (9).
In fact, the cyclic pitch mechanism (11) has arms (13) for transmitting a force which causes longitudinal inclination of the oscillating plate (9) and an arm (14) for causing side inclination of the latter engaged to a command arm (15).
This type of conventional command, applied to what is known as articulated rotor, when the cyclic control command (11) is actuated from the cabin, allows that the oscillating lever (9a), to which they are connected by means of strips (8') and blades (3) by means of linkages, moves or inclines in the desired way. Blades (3) will also follow the inclination of the oscillating plate (9a), fluttering until obtaining a position inclining the rotative disk such that the desired movement is obtained.
The operation of the collective pitch command (12) increases or diminishes the pitch of blades (3), regardless of the position thereof on the rotatory or sweep disk since the oscillating plate (9) will raise or lower on the rotational axis and displacing the connecting rods (8), connected to the blades (3) in an identical way, thus maintaining them parallel to the rotational axis of the mast (4).
The mechanism disclosed and schematically represented in FIGS. 13 and 14 is exterior and concentrical to the shaft transmitting the toroidal power to the wings of the main rotor and, therefore, the use of great diameter bearings is required. Further, the pivotating spherical body of the oscillating plate is of large size in order to allow the passage of the shaft through its center.
In these mechanisms, the need of using selflubricated mechanisms and a spherical body as pivot for the movable part, increases the friction of the command mechanism.
The size of the mechanism called "oscillating plate", presents a rotatory mass producing gyroscopic effects when rotating in a different plane. In fact, control rods transmitting movements of the control levers in the cabin, actuate the blades up to a point 90 degrees forward the place in which the desired displacement will take place due to the gyroscopic movement.
Blades, when operating quickly, act as a gyroscope and offer a resistance at a point located 90 degrees towards the rotational direction in which a torque or force is applied. In this way, when the cyclic control moves, this movement will be transmitted by means of linkages to the rotors, and a force at a determined point of the rotational plane is created, with respect to the point in which the force is applied.
This gyroscopic effect is noted at the commands, disturbing the stability of the helicopter and, therefore, an additional effort at the commands is required. In order to overcome this disadvantage, servocommand (16) or friction damper (17) systems are used, FIG. 15, in order to restrict movement of the blades and maintain the center of gravity without any variation, in order not to produce excessive vibration affecting the helicopter buoyancy during flight.
In most helicopters, a stabilizing bar is also employed in order to prevent instability, this bar rotating exactly below the articulated rotors and, acting as a gyroscope maintaining the rotational axis, thus avoiding oscillations disturbing the machine.
The conventional command mechanism called "oscilating plate", as may be seen, has certain disadvantages, although it fulfills the specific object, but the cited disadvantages leading to disturbances in the helicopter stability, have caused the use of friction dampers or stabilizing bars in order to avoid excessive vibration due to possible changes in the center of gravity of the system.
Therefore, designers are very much concerned about the asymmetrical buoyancy problem obtained by the use of a proper positioning of the attack angle of the blades which, at present, is obtained by means of said mechanism which, due to its size, requires additional efforts at the commands to counteract the mentioned effects.